Wireless communication systems can provide a number of different voice communication services, including interconnect voice communication services and dispatch voice communication services. Interconnect voice communication services are those that are provided by most wireless communication systems, and are commonly considered as full-duplex, circuit-switched communications. Dispatch communication services are provided in only some wireless communication systems, and are commonly referred to as push-to-talk or walkie-talkie calls due to the half-duplex nature of the calls.
Dispatch communication services have typically been provided only in private wireless networks. For many years wireless networks based on the iDEN standard were the only publicly-accessible wireless networks that provided both dispatch and interconnect communication services. Recently wireless networks based on other wireless communication standards have incorporated dispatch communication services in addition to interconnect communication services. These newer dispatch communication services are based on, for example, Open Mobile Alliance (OMA) Push-to-Talk over Cellular (PoC) standards-based protocols.
One characteristic of the iDEN network is that it provides guaranteed talk permit and forced audio for dispatch communications. Guaranteed talk permit means that when a dispatch communication is setup the network verifies that the terminating communication unit is available (i.e., is registered with the network and radio frequency resources are available) and provides a confirmation tone to the originating communication unit. The user of the terminating communication unit is not typically involved in the call setup process. The originator of the communication can then send audio to the terminating communication unit, and this audio is automatically output without any action on the part of the user of the terminating communication unit. Hence the name forced audio.
The PoC standard provides three different call answering modes, auto answer, manual answer and manual answer override, none of which provide guaranteed talk permit with forced audio. FIG. 1 is a call flow diagram of an exemplary call setup procedure for a terminating communication unit set in auto answer mode in accordance with the PoC standard. The entire call setup procedure as defined by the PoC standard is illustrated in FIG. 1, however, only those portions relevant to understanding the present invention are presented here. For a more detailed discussion of the PoC standard the interested reader can refer to the document entitled Push-to-Talk over Cellular (PoC) Architecture V2.0.8 (2004-06), the entire disclosure of which is herein expressly incorporated by reference.
As illustrated in FIG. 1, when a terminating PoC server receives a session initiation protocol (SIP) INVITE message from an originating communication unit for a terminating communication unit set in auto answer mode (step 102), the terminating PoC server automatically responds with a SIP 200 OK message (step 104). This response is automatically generated without determining whether there are radio frequency (RF) resources available for the terminating communication unit. Auto answer is what is commonly referred to as optimistic talk permit, in that the terminating PoC server automatically indicates that the dispatch communication can proceed without determining whether the terminating communication unit can actually be provided with radio frequency resources. This can result in an originating communication unit sending audio to the terminating communication unit, only to find out that the communication was not actually setup due to, for example, the lack of radio frequency resources for the terminating communication unit, the terminating communication unit not being in a radio frequency coverage area of the network, or the terminating communication unit not being powered-on.
FIG. 2 is a call flow diagram of an exemplary call setup procedure for a terminating communication unit set in manual answer mode in accordance with the PoC standard. As with FIG. 1, the entire call setup procedure as defined by the PoC standard is illustrated in FIG. 2, however, only those portions relevant to understanding the present invention are presented here. As illustrated in FIG. 2, manual answer requires that the user of the terminating communication unit actually indicate that they wish to take the call by, for example, actuating a particular button on the communication unit (step 202). Although this provides guaranteed talk permit, it does not provide forced audio because the user of the terminating communication unit is aware that the call setup procedure is occurring and must affirmatively consent by, for example, actuating a button on the communication unit to actually participate in the communication.
Manual answer override is a calling mode set by an originating communication unit indicating that even if the terminating communication unit is set to manual answer, the terminating PoC server will respond to the originating PoC server that the terminating user is available, before the terminating PoC server has determined whether radio frequency resources are available to support the terminating communication unit
Because the iDEN network was optimized to support both interconnect and dispatch communications, the network could provide a dispatch call setup with guaranteed talk permit and forced audio in less than one second. Networks designed in accordance with the PoC standard, however, are not optimized for dispatch communications, and accordingly various techniques are employed to provide a similar feel to the less than one second call setup time that is provided by the iDEN network. One of these techniques is the auto answer mode, which, as described above, indicates to the originating communication unit that the communication has been setup, even before making this actual determination. This provides the user of the originating communication unit with the feeling of a fast communication setup, but can greatly disappoint a user when the communication fails. In contrast, the manual answer answering mode provides guaranteed talk permit, but does not provide the fast communication setup provided by the iDEN network.